The invention relates to a process for purifying a stream of mechanically comminuted material, such as chips from wood cutting and sawdust, as well as for enriching fine ores and other minerals by mechanical sorting. With prior art processes the thickness of a material stream is enlarged under shaking and the lower layer of the material stream is enriched with heavier or smaller particles, respectively, due to the effect of gravity. The upper layer containing lighter or bigger particles, respectively, is then separated by means of a mechanically active separating or cutting means.
According to a suggestion not yet belonging to the prior art, the stream of raw material is subjected to a mechanical purification without the addition of a liquid, and two fractions are created in a dry sorting manner. The heavier particles form the lower layer and the lighter particles form the upper layer. In the above mentioned process, in which the separating means are formed as a horizontal disc arranged above the level of the bottom opening, depending on the material to be processed it may happen that the material builds up and the removal of the lower stream of material is disturbed, especially when materials of a higher specific gravity (such as fine ores) have to be treated. It is desireable to be able to control the removal speed for the lower material stream and to adapt it to the processing of materials of various specific gravities.